A conventional round of ammunition typically has a rimmed case supporting a projectile. When the round is inserted into the breech of a gun tube, the rim on the case engages a groove defined in the breech end of the gun tube that ensures that when the breech is closed, the round is correctly positioned relative to a breech face for the primer of the round to be struck by the firing pin during firing of the gun. This positioning is irrespective of the elevation or depression of the gun tube.
Mortars have for years used caseless ammunition, but to ensure that the round is in contact with the breech for firing, the barrel is always angularly elevated. Many types of modern ammunition are caseless, having a separate projectile and modular propellant components. An advantage of such ammunition is that the number of modular propellants may be varied depending upon the range over which the projectile is desired to be fired. A problem with such ammunition is that, without a case, there is no rim to correctly position the round relative to the firing pin when the breech assembly is closed. Without such rim, the modular propellant may be spaced apart from the breech assembly face when the breech assembly is closed, especially if the barrel is only slightly elevated or is angularly depressed. In such disposition, the firing pin may not reach the primer of the modular propellant or may not reach the primer with sufficient force to ignite it, resulting in a dud or misfired round.
There is a need then in the industry to provide a reliable system of ensuring that rimless ammunition is regularly seated against the breech face of the breech assembly prior to filing of the round. There is further a need to provide a simple mechanism by which to control both the firing pin and the valve; speed, timing and control must be easily obtained through a simple rotational or linear movement.